In air conditioning systems such as those used on motor vehicles, there is typically provided an accumulator between the evaporator and the compressor. The purpose of the accumulator is to trap any liquid in the system against delivery to the compressor. The accumulator is also typically provided with a desiccant for trapping any water that may have entered the system. Thus, the accumulator serves as a protective device for the compressor.
In the accumulator, there is normally provided a U-shaped return tube along with a baffle. Entering refrigerant impinges upon the baffle, and any liquid such as liquid refrigerant, water, and oil is separated out and deposits at the bottom of the accumulator while the gaseous refrigerant is permitted to pass to the compressor through an open end of the tube that is located near the ceiling of the accumulator. The above mentioned desiccant collects any water for permanent retention thereof while a bleed hole provided in the return bend of the tube near the bottom of the accumulator is operative to withdraw the liquid refrigerant and oil and return same in a vaporized form along with the refrigerant vapor passing through the tube.
Normally, there is one such oil bleed hole and it is of a fixed size (diameter) calibrated to provide a limited rate of oil bleed as discussed in more detail late r. However, it has been found that for better lubrication of the compressor under low refrigerant charge conditions, it is desirable to then somehow provide for more oil bleed to the compressor when lubricant demands are then most severe as otherwise the oil return would normally fall off under such conditions.